Clinical and Laboratory Diagnosis of Prader-Willi Syndrome:

Prader-Willi syndrome is a disorder of structural and functional alterations including developmental, behavioral, neurologic, endocrine, and structural abnormalities, that is due to dosage imbalance of the genes on 15q11-q13 relating to genetic imprinting in that region. Most of features of Prader-Willi syndrome are nonspecific and vary with age, genetic basis, race, and other unknown factors. A number of other disorders can have similar features, depending on the age of the patient. Clinical diagnostic criteria were developed in 1993 that can aid the clinician and researcher in determining whether definitive diagnostic testing is indicated. Methylation analysis, which determines whether or not relevant genes in 15q11-q13 are active, can be used to confirm or exclude the diagnosis in an affected patient. When these genes are inactive, which usually occurs when only maternally inherited genes are present, Prader-Willi syndrome results. For genetic counseling purposes, it also is possible to determine whether the disorder is due to a deletion in the paternally inherited 15q, maternal uniparental disomy 15, or a defect in the imprinting process. High-resolution chromosome analysis is useful to determine whether there is a translocation or other chromosome abnormality that caused the altered gene dosage.